<style type="text/css">
    .flex-grow {
        display: flex;
        flex-grow: 0;
    }

    .target1 {
        flex-grow: 1;
    }

    .target2 {
        flex-grow: 2;
    }
</style>
<div class="flex-grow">
    <p class="target1">Item
        <br>
        <strong>1</strong>
        <p class="target2">Item
            <br>
            <strong>2</strong>
        </p>
        <p>Item
            <br>
            <strong>0</strong>
        </p>
</div>